UNIVERSITY OF NEW SOUTH WALES

School of Civil Engineering

M ASSESSMENT OF NETWORK MODELS

FOR FLOOD FORECASTING

Name: T. A. Malone

Award: Master of Engineering Science

Year of Submission: 1989

Supervisor: Dr I. Cordery UNIVERSITY OF N.S.W.

- 3 OCT 1990

LIBRARY 1. STUDENT’S DECLARATION

a. This is to certify that I, ....S...... , being a candidate for the degree of Master of Engineering Science am fully aware of the policy of the University relating to the retention and use of higher degree projects, namely that the University retains the copies of any thesis submitted for examination, "and is free to allow the thesis to be consulted or borrowed. Subject to the provision of the Copyright Act (1968) the University may issue the thesis in whole or in part, in photostat or microfilm or other copying medium". I also authorize the publication by the University Microfilms of a 600 word abstract in Dissertation Abstracts International (D. A. I.).

b. I hereby declare that none of the work in this project has been submitted to any other institution for the award of a higher degree.

2 SUPERVISOR’S CERTIFICATION

I certify that this project has been completed under my supervision and is in my opinion in a form suitable for examination as part of the requirement for admission to the degree of Master of Engineering Science. AN ASSESSMENT OF NETWORK MODELS

FOR FLOOD FORECASTING

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

Section Page

1. INTRODUCTION 1

2. CATCHMENT DESCRIPTION 5

2.1 Tweed River to Murwillumbah 5

2.2 Wilsons River to Lismore 8

2.3 Macleav River to Kempsev 11

3. DATA COLLATION AND PREPARATION 15

3.1 Rainfall Data 16 3.2 River Data 18

3.3 Selection of Flood Events 19 3.4 Baseflow Separation 21

3.5 Rainfall Loss Model 23

3.6 Rainfall Distribution 24

4. CATCHMENT MODELS 26

4.1 Unit Hvdrograph 27

•4.2 RORB 27

4.3 WBNM 32

4.4 Model Comparison 36

4.4.1 Unit Hvdrograph vs Network Models 36 4.4.2 RORB vs WBNM 37 5. METHODOLOGY 39 5.1 Model Calibration 39

5.1.1 Rainfall Losses 39

5.2.2 Unit Hvdrograph 41

5.1.3 Network Models 44

5.2 Results 48

6. DISCUSSION 51

6.1 Rainfall Distribution and Losses 51 6.2 Model Performance 53

6.3 General Discussion 59

7. CONCLUSIONS AND RECOMMENDATIONS 62

REFERENCES

APPENDICES

A - Rating Tables

B - Wilsons River to Lismore

Unit Hydrograph Derivation

C - Macleav River to Kempsev Typical RORB & WBNM Calibrations

D - Summary of Results List of Tables Page

2.1 Flood Level Classifications 8 3.1 Floodwarn Networks 16 3.2 Selected Flood Events 20

5.1 Initial and Continuing Losses 40

5.2 Unit Hvdrograph Peak Times 42

5.3 Three Hour Unit Hydrographs 43

5.4 Model Calibration Parameters 46

5.5 Summary of Model Results 49

List of Figures Page

2.1 Tweed River - Catchment Map 6 2.2 Wilsons River - Catchment Map 9 2.3 Macleay River - Catchment Map 12 3.1 Baseflow Separation 22

3.2 Initial Loss - Continuing Loss Model 23 4.1 Tweed River - RORB Network 28 4.2 Wilsons River - RORB Network 29

4.3 Macleay River - RORB Network 30

4.4 Tweed River - WBNM Network 34 4.5 Macleay River - WBNM Network 35

-5.1 Tweed River - RORB Parameter

Indifference Curves 45

6.1 Tweed River - Model Results 57 ABSTRACT

Two similiar non-linear network models have been applied to three catchments in coastal NSW to examine their potential for use in operational flood forecasting. Network models have the potential to make direct allowance for non-uniform catchment response to input rainfall. The two models, RORB and WBNM, were applied under operational forecasting conditions to data for 7 to 8 flood events on each catchment and their ability to reproduce the observed hvdrographs was compared with the unit hydrograph approach which is curently used for flood forecasting in each catchment.

The results indicate that the determination of excess rainfall is probably more critical than the type of model used to calculate the direct runoff hydrograph. There appears to be little difference between the abilities of the unit hvdrograph and the network models to reproduce the observed hvdrographs on the three catchments which ranged in size from 630 square kilometres to 10,000 square kilometres. However overall, the network models offer a number of advantages over the unit hydrograph for flood forecasting. AN ASSESSMENT OF NETWORK MODELS FOR FLOOD FORECASTING

1. INTRODUCTION

Under the Meteorology Act of 1906, the Commonwealth

Meteorologist was given the responsibility, amongst other things, for 'the display of .... flood signals' and in that year the Bureau commenced the issue of generalised flood warnings. However, it was not until a series of highly damaging floods in NSW in the mid-1950s that a Hydrometeorological Service was established in the Bureau with one of its main aims being to provide systematic flood forecasts.

Flood forecasts provided by the Bureau include both qualitative and quantitative forecasts. Qualitative forecasts are statements of expected occurences of a flood event in the broad descriptive classes of minor, moderate and major flooding. Quantitative forecasts are the ultimate aim of the Bureau of Meteorology flood forecasting service providing height predictions at key river gauges in a catchment, with a pre-determined degree of accuracy and lead time.

The classification of flooding at a key river gauge is based on the following definitions:

Minor Flooding - This causes inconvenience such as cutting of minor roads and submergence of low level bridges and makes the removal of river pumps necessary. Minor flooding causes little inundation of land adjacent to the river.

1 Moderate Flooding - This causes inundation of low­ ly ing areas requiring the removal of livestock and the evacuation of isolated houses. Main traffic bridges may be closed.

Major Flooding - This causes inundation of large areas, isolating towns and cities. Major disruption occurs to road and rail traffic and other communications.

Evacuation of many houses and business premises may be required.

The most important requirement of a flood forecasting system is to provide the maximum lead time of a river reaching a specified height at a specified time at a particular location.

Based upon this requirement, different types of flood forecasting systems are employ ed on different sized catchments. In smaller catchments these tend to be rainfall based methods whilst in the larger catchments river routing techniques tend to be employed. Often a combination of these techniques is used to predict downstream flood heights.

When the Bureau commenced providing quantitative flood forecasts in small river basins, the unit hydrograph was the only rainfall based hydrologic model readily available.

Often during floods, real time rainfall information available was limited to a relatively small number of stations which reported at three hourly intervals to the

2 Bureau. Operational requirements dictated that flood predictions, based on the latest observations from these stations, were broadcast to the public every three hours.

Frequently flood forecasts were required for more than one river at a time when computing ability and facilities were very limited. Under these conditions, the unit hydrograph proved to be ideal as it was robust and simple to use. As a consequence, approximately 50 were derived by the

Bureau for flood forecasting operations in NSW.

The advent of computers and their increasing availability has seen the more widespread use of rainfall­ routing or network models, especially in probabilistic hydrology. As yet, they have found limited use in operational hydrology.

The purpose of this study is to determine if network models give more accurate and consistent results than unit hydrographs when used to forecast floods of different magnitudes.

Two similar non-linear network models, RORB and WBNM, will be compared with the unit hydro graph on three catchments under similar conditions to operational use.

The quantity and quality of the data used and the assumptions made during this investigation are similar to those which occur in operational flood forecasting. This important underlying aspect of the study cannot be emphasised strongly enough.

3 The three catchments selected for investigation are ir coastal NSW and are of varying sizes. The Tweed River tc Murwi 1 lurnbah has a catchment area of about 630 square kilometres, the Wilsons River to Lismore an area of 140C square kilometres and the Macleay River to Kempsey is mucl larger with a catchment area of 10,000 square kilometres.

Flooding is a problem in each of these catchments and unit hydrographs have been used regularly in past floods to forecast heights at critical locations with varying success.

4 2. CATCHMENT DESCRIPTION

2.1 TWEED RIVER TO MURWILLUMBAH

The Tweed River to Murwillurnbah, located on the northern NSW coast near the Queensland border, comprises the catchment areas of the Tweed River and the Oxley River and the smaller catchment of Dunbible Creek. The total catchment area to Murwillurnbah, shown on Figure 2.1, is 630 square kilometres.

Mt Warning, a 1150 metre remnant core of a volcano, dominates the catchment with a symmetrical drainage pattern emitting from it.

The northern arm, the Oxley River, rises in the rugged

MacPherson Ranges at elevations between 900 and 1100 metres. A number of small tributaries converge before flowing eastward and joining the Tweed arm about 7 kilometres upstream of Murwillurnbah.

The southern arm is the Tweed River which rises in the mountain range in the south between elevations of 600 to 900 metres. Various tributaries drain northward before joining the main watercourse which then flows eastward to Murwillurnbah.

Dunbible Creek which drains the eastern slopes of the valley joins the Tweed River just upstream of Murwillurnbah.

Over sixty percent of the Tweed valley is hilly to mountainous. The main streams in the valley above

5 • Rain Station A River Station

0 2 4 6 8km

COMPILED DRAWN BASIN No. 201 TAM TWEED RIVER FIGURE DATE DRAWN DATE AMENDED CATCHMENT MAP 2-1

6 Murwillumbah flow through small narrow valleys. As a consequence, the terrain is still being actively eroded and the limited areas of alluvial flats are located mainly in the lower reaches of the two main arms. Much of the original rainforest still exists around the edges of the valley and in the Tweed arm but elsewhere the land has been cleared for pastoral use.

In those cleared pastoral areas, the main activity is dairying, especially in the lower reaches of the Oxley River. The main agricultural use occurs downstream of Murwillumbah but there is some bananna growing on the steeper slopes above Murwillumbah. There is also some limited small scale commercial forestry in the valley.

Whilst the main flooding problem occurs below

Murwillumbah, the township itself is subject to regular flooding. Since the establishment of the flood gauge at Murwillumbah in 1928, there were 11 occasions up to 1976 when the major flood level, given in Table 2.1, was exceeded.

The frequent occurrence of floods in the late summer reflects the fact that the main flood producing storms are tropical cyclones rather than winter depressions.

Rainfall totals during floods can be as high as 650 mm with variations as much as 50% across the catchment.

7 TABLE 2.1 FLOOD LEVEL CLASSIFICATIONS

Gauge height in metres

Station Minor Moderate Major

Murwillumbah 3.0 4.0 4.8 Lismore 5.0 8.0 10.5

Kempsey 4.0 5.5 6.5

2.2 WILSONS RIVER TO LISMORE

The Wilsons River to Lismore is located slightly inland from the coast immediately south of the Tweed

River. The total catchment area to Lismore is 1400 square kilometres.

The river system above Lismore, shown in Figure 2.2, is unusual in that it has a fan shaped drainage pattern with three distinct drainage areas. All three rise in the elevated ranges about 1200 metres above sea level to the north of Lismore and radiate southward.

The Wilsons River catchment drains the eastern most part of the catchment flowing initially southward and then westward toward Lismore. • The Leycester Creek system drains the western portion of the catchment and flows generally southeasterly where it joins Terania Creek just above Lismore and then the Wilsons River at Lismore itself. The Terania Creek system drains the central part of the catchment.

The three drainage systems have roughly the same catchment area and, individually, can be responsibile for

8 flooding at Lisrnore. The fan shaped drainage pattern tends to concentrate runoff quickly and peaks from the three systems can arrive simultaneously at Lisrnore.

Similarly to the Tweed valley, the soils in the

Wilsons valley are volcanic in origin and it is this origin which is responsible for the rugged characteristic of the central part of the catchment. The eastern and western areas tend to be less hilly.

In the upper reaches, thick rainforest, which once covered the majority of the catchment, is still found whilst in the lower reaches, much of the vegetation has been removed and is now covered by pastoral grasslands.

Lisrnore has been subject to regular serious flooding since it was first settled. Major floods, as defined in Table 2.1, occur about once a year. Historically, Lisrnore is probably the most flood prone town in Australia with seventy one large floods being recorded in the valley since 1900. Large areas of the town are inundated during such events with 1900 residences, 680 commerical properties and 26 industrial enterprises classified as flood prone.

As with the Tweed valley, there is a strong seasonality with the main flood events occurring between

February and September due to the pre-dominance of tropical cyclones. Rainfall over the catchment shows a marked temporal and spatial variation with totals during floods up to 450 mm recorded in the eastern part of the

10 catchment and as little as 25 mm in the western part.

2.3 MACLEAY RIVER TO KEMPSEY

The Macleay River to Kempsey, located on the northern

NSW coast as shown in Figure 2.3, is much larger than the

Tweed and Wilsons Rivers draining an area of some 10,000 square kilometres. It is bounded by the Great Dividing

Range in the west rising up to 1200 metres and ranges in the north and south which rise up to 1600 and 1300 metres respectively. The catchment to Kempsey can be roughly divided into three sections; tablelands above an approximate line along the Styx and Apsley Rivers, gorge country in the centre of the catchment and slopes becoming more gentle as the river approaches Kempsey.

The tablelands area is drained by three main tributaries which join near the gorge country.

The Apsley River is the principal river in the south eastern part of the catchment and accounts for about 25 percent of the catchment area to Kempsey. Similarly, the Muddy River catchment which drains the central part of the tablelands around Guvra and Armidale, accounts for about

25 percent of the catchment to Kempsey. The Chandler

River drains the more rugged northern part of the tablelands but only accounts for about 15 percent of the total catchment area.

Below the junction of these three main tributaries the

Macleay winds through some very rugged but spectacular gorge country. This area accounts for about 25 percent of

11 the total catchment area and is drained by a number of smaller creeks such as Dungay, Nulla Nulla, Majors and Hickeys Creeks.

The significance of the area drained by each of these systems can be readily seen by examining the rainfall distribution. There is considerable variation across the catchment with the west receiving about 750 mm per year, the north 1500 mm, the south 1200 mm and Kempsev itself

1100 mm. The heaviest rainfalls tend to be below the tablelands area and in the Macleay Valley flood study

(Public Works Dept of NSW 1980), it is sugggested that this zone contributes most of the flood runoff to Kempsev even though it accounts for only 30 percent of the catchment area.

The tablelands area is mainly used for agricultural purposes such as beef cattle and wool sheep with some intensive cropping of maize, oats and lucurne in the far western areas. Land use in the rugged central part of the catchment is restricted to timber getting while the lower area supports dairying, beef cattle and associated fodder crops.

Historically, some of the most damaging floods which have occurred on the NSW coastal rivers have been recorded in the Macleay River. Since 1949, there have been at least 14 floods above the minor flood level given in Table 2.1. The highest was in 1949 when the river reached a gauge height of 7.92 metres.

13 There are clearly two periods in which most flooding occurs. In the early part of the year from January to

April, floods tend to be produced from tropical cyclones originating in the north while in the June to August period the main flood producing mechanisms are low pres­ sure systems which form in inland NSW and move towards the coast where they receive an inflow of moist tropical air.

It is interesting to note that whilst the incidence of flooding is less in the later part of the year, the severity of flooding tends to be greater.

14 3. DATA COLLATION AND PREPARATION

The first step in the modelling process is the collection of historical data. During this process a number of problems became apparent. Often the data most desired were either not recorded, lost or simply non­ existent. Eventually the data used represented a compromise thereby weakening the basis of the modelling process.

This is the situation with the rainfall and river height data in the three catchments under investigation.

In forecasting floods in the Tweed, Richmond and

Macleav catchments in the past, the Bureau of Meteorology was largely dependent on a network of manual rainfall and river height readers in each catchment. Whilst more recently this manual network has been supplemented by both telephone and radio telemetry, the manual observers still form the basis of the reporting networks.

Details of the rainfall network and the river height stations used in each of the study catchments is given in Table 3.1 while the location of the stations in the Tweed,

Wilsons and Macleav catchment is shown in Figures 2.1, 2.2 and 2.3 respectively.

The manual readers report, via telephone, to the

Bureau at three hourly intervals with observations. In the case of rainfall stations, readings were generally from standard 200mm diameter rain gauges or from tipping bucket rain gauges with a digital readout display whilst

15 river heights were usually taken from a staff gauge at the critical location.

TABLE 3.1 FLOODWARN NETWORKS

Catch­ Rainfall Network River Station ment Bureau No Name AWRC No Name

Tweed 058011 Chillingham 058129 Kunghur 058158 Murwillumbah 201902 Murwillumbah

Wilsons 058146 Kyogle 058044 Nimbin 058072 Federal 058037 Lismore 203904 Lismore Made ay 056002 Armidale 057017 Jeogla 056035 Walcha 057052 Lower Creek 057037 Tia 059000 Bellbrook 059017 Kempsey 206402 Kempsey Traffic Br

3.1 RAINFALL DATA

Typically, the rainfall stations in the flood warning networks have no on-site recording equipment to check three hourly rainfall readings and the only available historical records are daily rainfalls totals. Relatively few stations had pluviographs and the only available detailed rainfall records consist of those rainfalls which were reported to the Bureau during the actual event and recorded in unoffical flood case historys within the Bureau.

Another limitation is that the rainfall network does not necessarily give a good indication of actual catchment rainfall. Because the rainfall network consists of manual

16 observers, the stations are not necessarily in the most ideal location to give the best rainfall coverage. It is usually a case of finding someone willing to provide rainfall data in locations that may not be the most desireable.

The rainfall stations used in the study are generally those that made up the flood warning network at the time of the flood. Since this time there have been amendments and additions to the network which have resulted in more reliable information and a better coverage of the catchments.

From Figure 2.1, it can be seen from the rainfall network used in the Tweed catchment that the three stations used do not give a good coverage of the catchment. Chillingham is well outside the catchment and may not reflect rainfall within the catchment. On the other hand, the seven rainfall stations within the Macleay catchment give excellent coverage of the perimeters of the catchment but as the centre of the catchment is uninhabited, no information is available for this area.

At the time of the selected flood events, these were the only stations available and, as indicated in the introduction, they will be used in the study.

The initial rainfall reading from many of the manually read gauges created another problem. This value tended to be the cumulative amount of rainfall since the previous 9am. In the absence of any other information and in the interest of expediency, it was generally assumed

17 that this rainfall was evenly distributed back to the previous 9am. This assumption usually did not have a signficant effect as this rainfall tended to be accounted for by initial loss.

3.2 RIVER DATA

Problems were also encountered with data from the critical river height stations in each of the three catchments.

The forecast point in the Tweed catchment is the staff gauge at the Murwillumbah; Height readings at this station are taken by a manual observer and, as with the majority of rainfall stations in the flood warning networks, there is no on-site recording equipment at this site to check the historical readings. It is known that low flows at this station are affected by tides.

Another more serious complication is that of rating at the station. The Tweed River at Murwillumbah Bridge has long been used as the forecast point for the catchment and a rating table for the site exists. However the source of this table and its accuracy are not known.

Similarly, the Wilsons River at Lismore is a manually read station with no recording equipment and has a rating table of unknown origin and accuracy.

The situation on the Macleay River at Kempsey Bridge is a little better with the site being telemetered,

18 recorded on-site and known to have been gauged giving some degree of confidence in the rating. Similarity to the station on the Tweed River at Murwillumbah, low flows at this point on the Macleay River are tidal affected.

Copies of the rating tables for each of the river stations used in the study is included in Appendix A.

Whilst it is assumed that both the rainfall and river height readings are taken at precisely the three hour intervals, very often they may be taken within half an hour of the reporting time. Often telephone difficulties encountered during floods meant that rainfall observations were often reported less frequently than the requested three hourly interval. Being manual observations, there is no way the historically recorded values can be checked and this should be kept in mind when discussing the results of the study.

3.3 SELECTION OF FLOOD EVENTS

Flood events selected for use in the study were limited to those which occurred in the last 25 years.

This was for two reasons. Firstly, the effect of changes in catchment conditions was likely to be minimised and secondly, the data, being relatively recent, was more readily accessible. Table 3.2 summaries the flood peaks of the events selected. Note that the peak flows given in these tables are the total peak flows.

19 TABLE 3.2 SELECTED FLOOD EVENTS

(a)Catchment: Tweed River to Murwillumbah

Event Date Class Peak Ht Peak Flow No (m) (ra3/s)

1 10/05/87 Major 5.20 1370 2 05/03/87 Moderate 4.10 900 3 09/04/84 Moderate 4.50 1060 4 09/05/80 Moderate 4.39 1020 5 * 13/03/78 Major 5.24 1390 6 * 11/02/76 Major 5.00 1270 7 11/03/74 Major 5.82 1680 13/03/74 Moderate 4.55 1090 8 * 26/01/74 Major 5.38 1460 9 14/02/73 Moderate 4.67 1140 10 28/10/72 Moderate 4.57 1090 29/10/72 Moderate 4.24 955

(b)Catchment: Wilsons River to Lismore

Event Date Class Peak Ht Peak Flow No (m) (m3/s) 1 11/05/87 Major 11.50 1440 2 06/03/87 Major 11.20 1340 3 10/07/85 Minor 7.88 510 4* 01/11/84 Minor 7.30 410 5 09/04/84 Major 10.60 1150 6 * 21/02/81 Minor 6.30 280 7 19/03/78 Major 10.90 1240 8 * 29/02/76 Major 10.92 1250 9 12/02/76 Moderate 8.40 610 10 03/03/75 Major 11.35 1385 11 21/01/74 Moderate 9.91 950

20 TABLE 3.2 SELECTED FLOOD EVENTS(contd)

(c)Catchment: Macleay River to Kempsey

Event Date Class Peak Ht Peak Flow No (m) (m 3 / s)

1 14/06/67 Moderate 6.08 4070 2 13/01/68 Moderate 5.77 3490 3 * 19/02/71 Minor 4.55 1870 4 09/01/74 Moderate 5.58 3230 11/01/74 Moderate 5.17 2650 12/01/74 Moderate 5.14 2610 5 * 11/03/74 Moderate 5.69 3380 13/03/74 Moderate 5.66 3340 6 13/11/75 Minor 4.10 1480 15/11/75 Minor 5.15 2620 7 * 12/02/71 Moderate 5.51 3130 8 19/05/77 Minor 5.47 3080 9 20/03/78 Minor 5.01 2440 10 10/05/80 Moderate 5.73 3380 11 11/07/85 Moderate 5.59 3110

* - test events

The floods selected in each catchment ranged from minor to major events. In this way the ability of each model could be tested over a range of flood magnitudes.

Event 7 in the Murwillumbah catchment and events 4, 5 and

6 in the Macleay catchment are multipeaked events.

A number of events in each catchment were not used in

the calibration process but reserved to test the derived parameters. These are indicated in Table 3.2 as test

events.

3.4 BASEFLOW SEPARATION

As each of the models can simulate the direct runoff process, it was necessary to determine the direct runoff hydrograph for each flood event.

21 DISCHARGE proportion charges any at 104 0.01 (1975)

the

of m3/s In m3/s

maximium, the determined NSW

in

FIGURE in

per

selected of NSW rivers the

km2 the

coastal

Tweed, 3.1

is

.

that

total

only This events baseflow ■Assumed

TIME BASEFLOW

Wilsons

catchments 90%

hydrograph. about translates 22

baseflow Observed of

is SEPARATION and 5% the

of usually hydrograph investigated

Macleav maximium

to the

Klassen 6

m3/s, peak

catchments

a

baseflow

very discharge

and 14 were

m3/s

Pilgrim

small

below

dis and,

and in

­

Baseflow separation is not critical and a baseflow consisting of a straight line between the commencement and cessation of direct runoff, as shown in Figure 3.1, was assumed.

The same assumption is made under operational conditions when a constant baseflow, equal to a value of flow at the time of rise of the total runoff hydrograph is assumed.

3.5 RAINFALL LOSS MODEL

The initial loss - continuing loss (IL-CL) model, shown in Figure 3.2, is the model most commonly used in

Australia for converting gross rainfalls to excess rainfalls in rural catchments.

Initial loss

Continuing loss

FIGURE 3.2 INITIAL LOSS - CONTINUING LOSS MODEL

23 During floods, initial loss is usually estimated from antecedent moisture conditions in small catchments while in larger catchments, where the lead time is relatively long, the initial loss can be estimated from the time of commencement of rise of the flood hvdrograph. In this study initial loss was estimated during the calibration process such that the time of the initial rise in the hydrograph was matched.

Actual continuing loss rates can only be determined after the event when the full hvdrograph is known and the rainfall and runoff volumes can be matched. During operational flood forecasting, the continuing loss rate used is usually the median value derived from a number of past events.

3.6 RAINFALL DISTRIBUTION

In allocating rainfall in each model, it was decided to adopt a procedure similar to one which would be used in real time operations. This precluded the use of any isohvetal method based upon total storm rainfalls as the allocation of rainfall from the reporting stations within each model must be pre-determined.

For the unit hydrograph, the average catchment rainfall is firstly determined by averaging the observed rainfalls period by period according to their Thiessen weights . The IL - CL model is then applied to this average gross rainfall , leading to the inference that runoff commences a t the same time throughout the

24 catchment.

In the RORB model, each sub-area was allocated the rainfall depth and temporal pattern of the nearest reporting rainfall station, the nearest rainfall station being determined by Thiessen polygons.

The allocation of sub-area rainfalls in WBNM is a little more complex but perhaps more realistic than RORB.

WBNM calculates each sub-area rainfall, period by period, based upon the Thiessen weights of all relevant rainfall stations. Thus in say the Macleay model each of the 46 sub-areas required Theissen weights for the 7 rainfall stations in the reporting network.

However, despite these small differences between RORB and WBNM in the way rainfall were calculated for each sub-area, the application of the IL - CL model in each case is the same.

In the network models, a uniform IL - Cl model is applied to individual sub-area gross rainfalls. Thus in these models surface runoff is assumed to commence on different parts of the catchment at different times which is a different situation to the unit hvdrograph approach.

25 4. CATCHMENT MODELS

The unit hydrograph has been in widespread international use since it was first developed in the early 1930s. Network models, on the other hand, have been developed more recently and have found limited international acceptance.

The two network models used, RORB (Laurenson and Mein

1985) and WBNM (Boyd et al 1979), are both of recent origin. Each attempts to model the storage characteristics of a catchment by distributing the storage effect throughout the catchment. The distributed nature of storage is represented by a series of concentrated storages strategically located on the drainage network. As distinct from the unit hydrograph which is strictly a linear model, network models may be linear or non-linear, though it is more usual to use them as non-linear models. It is important to remember that all three models under consideration can only model surface runoff.

The modelling sequence in the two network models being considered is similar. The catchment is divided into sub-areas and each sub-area allocated a gross rainfall pattern. This gross rainfall is converted, via a loss model, into excess rainfall which, in turn, is converted to a surface runoff hydrograph from each sub- area. This surface runoff hydrograph is then routed through a conceptual sub-area concentrated storage using a power storage-discharge equation. Hydrographs from upsteam areas are stored whilst runoff is calculated from

26 other sub-areas. At stream confluences the appropriate hydrographs are summed and routed similiarly through downstream sub-areas until the whole catchment is modelled.

Whilst both models have been developed from the non­ linear storage model developed by Laurenson(1964), each varies slightly in its structure and in the way conceptual storages are treated.

4.1 UNIT HYDROGRAPH

The unit hydrograph needs little introduction but will be briefly reviewed for the puposes of completeness.

ARR(1987) defines a unit hydrograph ".... as the hydrograph resulting from unit depth of surface runoff produced by a storm of uniform intensity and specified duration."

Unit hydrograph theory is based upon two assumptions.

It is assumed that catchment response is linear, ie the ratio of inflow to and outflow from a catchment is fixed no matter what the size of the input. It is also assumed that the characteristics of a catchment which may affect its response to rainfall are combined into one model and the effects of particular characteristics cannot be identified.

4.2 RORB

In the RORB, rainfall excess is assumed to occur over the centroid of each sub-area and is converted into a

27 hydrograph by multiplying by the size of the sub-area.

This hydrograph is then routed through a sub-area storage, which is located midway between the centroid and the sub- area outlet, to produce a surface runoff hydrograph at the sub-area outlet.

The number of sub-areas in each of the catchments is in accordance with the recommendations of Boyd(1985) and the model structure for the Tweed, Wilsons and Macleay catchments are represented in Figures 4.1, 4.2 and 4.3 respectively.

The conceptual storage of each sub-area, represented as the triangles in these figures is assumed to be of the form;

S = 3600.k.Qm (4.1) where S = storage in m3 Q = discharge in rn^/s

m = a dimensionless exponent

k = storage delay time in hours

The exponent m is a measure of the catchments non­ linearity and the same value is used uniformly throughout the catchment. A value of 0.8 is recommended by the authors (Laurenson and Mein 1985) and is supported by other studies referred to in ARR(1987).

The value of k varies depending on the amount of storage between adjacent nodes. The assumptions that storage delay time is directly proportional to travel distance and that the average storage delay time for the

28 Sub-Area Area(km2)

Total

• Sub-Area Node

◄ Model Storage

O Junction Node

COMPILED TWEED RIVER BASIN No. 201 FIGURE DATE DRAWN DATE AMENDED RORB NETWORK 03 f 00 r-l CTl CT\

EhD>SX>^IS1^ RIVER

WILSONS nO^CO'TOiMHHOPIHn ■q’HOjifikDOH'xiHa'^Dionq'to ^'JOfflonciruoHhomeo criiocriiD'^'vxj'g'ijDocrirHro OJNrONfnH')'

'imuDUfcoXH^xjszo^aoiiotH Z> > £ X >* N couQWii.oa:H^«js:2 CQUQUfoOKH^t^JSZ

31 catchment is equal to catchment lag time lead to the storage for each sub-area being allocated according to Equation (4.2) .

The coefficient k is the product of two factors;

k = KC.KR (4.2) where KC = storage delay time of the whole catchment in

hours.

KR = a dimensionless ratio called the relative delay

time applicable to the storage in an individual

reach. This ratio is calculated from the

physical characteristics of the reach length

and average flow distance.

If m is assumed fixed, there is only one parameter,

KC, to be evaluated for the catchment and this is done by optimising the fit of calculated hydrographs with observed hydrographs.

4.3 WBNM

Watershed Bounded Network Model (WBNM), whilst being similar to RORB, is based on more geomorphological relations and has two different types of storage.

An ordered catchment, represented by an ordered catchment storage, is a complete sub-catchment and has no upstream area contributing to its runoff. An interbasin, represented by an interbasin storage, has an upstream area contributing flow to it as well as its own local area runoff. The difference between the two can be readily

32 identified on the WBNM networks for the Tweed and Macleay catchments on Figures 4.4 and 4.5 respectively.

WBNM treats the storage effects of each type of sub-area differently. The ordered catchment transforms the excess rainfall hvetograph to a hvdrograph of direct runoff at the end of the sub-area. An interbasin, as well as transforming the excess hyetograph on its own sub-area into a hydrograph, also has a transmission storage through which the upstream inflow is routed. The model assumes that these two components of runoff are subjected to different storage effects.

Storage is distributed in the WBNM solely on the basis of area. For the rainfall excess on a sub-area the storage equation is; S = C.A°*57.Q0-77 (4.3) where S = storage in m^ A = sub-area area in km?J Q = outflow discharge at downstream end of the sub-area in m3/s. C = dimensional empirical coefficient applicable to all sub-areas.

For routing of the upstream flows through interbasins the above equation is factorised by 0.6 to allow for a reduction in the amount of storage through which these flows are assumed to pass.

Similarly to RORB, if the exponent of Q is assumed constant, there is only one model parameter, C, to

33 O Ordered Basin

O Interbasin

COMPILED DRAWN TWEED RIVER BASIN No. 201 TAia FIGURE DATE DRAWN DATE AMENDED WBNM NETWORK 4-4 o

UDCTiCTiCT'rOcriOJrO ouno'iCT^o^^oaiHninn ojcsjncNjniH^rorn^rcMOJrHCvi^^oj r00]H^f03NHC30]fnH

«<£nuawt,OKi-i>-3u;js;zocuocc;wE-i^>sx>-'Ni OUQWtUSH^^JSZ CQOQUCj-iOKMI^ZJZZ

35 determine by the process of fitting calculated hydrographs to observed hydrographs.

4.4 MODEL COMPARISON'

4.4.1 UNIT HYDROGRAPHS VS NETWORK MODELS

There are two basic theoretical differences between the unit hvdrograph and the network model, both related to the assumptions underlying the unit hvdrograph.

Firstly, the unit hvdrograph is solely a linear model whilst the network models are usually used as non-linear models and secondly, storage in the network models is distributed against the lumped storage effect in the unit hvdrograph.

Practically, the treatment of rainfall varies significantly between the two types of model. For the unit hvdrograph, average catchment rainfall mustlv be determined before the rainfall loss model is applied.

Initial loss is assumed to be uniform over the entire catchment inferring that surface runoff commences at the same time at all points on the catchment. In the network models, the rainfall loss model is applied to the gross rainfall pattern allocated to each sub-area. If this pattern is sufficiently varied over the catchment, surface runoff is deemed to have commenced at differnt parts of the catchment at different times which is more likely than the unit hvdrograph senario.

36 4.4.2 RORB VS WBNM

Boyd(1983) identified eight significant differences between WBNM and RORB but as mentioned earlier, the major difference is related to the way in which storage is treated in each model. In RORB, storage routing occurs between nodes of adjacent sub-areas and outflow from the storage occurs at the downstream node whilst in WBNM, storage routing occurs within the sub-area and outflow occurs at the sub-area - outlet.

The allocation of storage in RORB is proportional to the stream length between nodes whilst the allocation of storage in WBNM is made solely on the basis of area.

RORB does not distinguish between sub-area runoff and runoff from upstream sub-areas and it routes these two components through the same amount of storage. WBNM, on the other hand, routes each component through a different amount of storage.

Two further practical differences were identified during this study in the area of rainfall allocation and model structure.

As discussed in the introduction, the models were used in the study in the same way they might be used for operational flood forecasting. Thus, in RORB, rainfall patterns and amounts were allocated on the basis of the nearest reporting rainfall station. WBNM adopts a more flexible approach by calculating sub-area rainfall on the basis of Thiessen weights for all available rainfall

37 stations. This method of determining sub-area rainfall would more likely give results closer to the preferred isohyetal method.

RORB appears to be more flexible than WBNM in setting up the catchment structures. WBNM does not allow any more than two sub-areas to be joined at a particular point, requiring the use of dummy sub-areas. The problem shows up in the model structures for the Macleay catchment,

Figures 4.3 and 4.5 respectively. In this catchment, more subareas were required to model the streamflow network for the WBNM model than for the RORB model.

38 5. METHODOLOGY

5.1 MODEL CALIBRATION

A similar calibration and testing procedure was followed in each catchment model for determining loss values and model parameters. In each of the three catchments, rainfall losses and the model parameters were derived for several floods. The median value of these parameters was then generally selected as the typical catchment parameter. The adopted parameters were then re-applied to the events used in their derivation and also tested on the smaller number of independent events.

In deciding typical parameters, the median value was generally adopted in preference to the average as it was felt that averages tend to be influenced by extreme values and may not be truly representative of the set of calibration parameters.

In the Tweed, 7 events were used for calibration and 3 for testing whilst in the Wilsons and Macleay catchments the number of events used were 8 and 3 respectively.

5.1.1 LOSSES

Prior to the determination of the model parameters, initial loss and continuing loss rates were estimated.

Initial loss was estimated so that the initial rise in the hydrograph was matched in each event.

Continuing loss rate was then computed such that the volumes of excess rainfall and surface runoff were equal.

39 In the program used to derive the unit hvdrographs and in

RORB , continuing loss rate is calculated automatically but in the version of WBNM used, the continuing loss rate was input by the user until rainfall and runoff volumes matched. However, there tended to be little difference between the loss rates in either of the network models.

As discussed earlier, each of the models handles rainfall distribution slightly differently so differences in initial loss and continuing loss rate should have been reasonably expected. This was proved to be the case, especially in the larger Macleay catchment. In the Tweed and Wilsons catchments there was little variation between the losses calculated in a given event across the three models. However, Table 5.1 shows that there was a significant difference between the losses calculated for the unit hydrograph and the network models in the Macleay catchment.

TABLE 5.1 INITIAL AND CONTINUING LOSSES

(a) Tweed River (b) Wilsons River

Event IL CL Event IL CL mm mm/h mm mm/h

1 0 14.0 1 70 0.9 2 65 7.3 2 75 2.7 3 140 1.5 3 50 3.8 4 0 2.9 4* - - 5* - - 5 120 0.1 6* - - 6* - - 7 0 2.1 7 115 3.0 8 * - - 8 * - - 9 55 4.2 9 80 0.8 10 40 4.5 10 35 3.3 11 70 0.6 Adopted Value 4.2 Adopted Value 2.0

40 TABLE 5,1(contd) INITIAL AND CONTINUING LOSSES

(c) Macleay River

Unit H graph Network

Event IL CL IL CL mm mm/h mm mm/h

1 20 1.5 20 2.2 2 80 2.7 80 3.3 3 * - - - - 4 80 0.4 80 0.6 5* - - - - 6 90 0.7 170 0.7 7 * - - - - 8 60 0.6 10 1.7 9 70 2.2 100 2.4 10 55 3.3 100 3.5 11 60 1.4 80 1.1

Adopted Values 1.5 1.9

* signifies test event

Though there are significant differences between the losses calculated for each use in each model, it is important to note that the depth of excess rainfall is the same for a given event. The differences are related to the way in which rainfall is allocated and excess rainfall determined in each model.

5.1.2 UNIT HYDROGRAPH

For each of the 'fit' floods in each catchment, a unit hvdrograph was derived using the method of least squares.

Of the numerous methods available, this approach is the one most commonly used to derive unit hvdrographs from complex storms where there is access to a digital computer. This may be because the method of least squares dampens out the effect of inprecision in the input and output data. However-, the method is sometimes unstable

41 and it is not uncommon for the derived unit hydrograph to contain unrealistic fluctuation or negative ordinates. This was indeed the case with most of the unit hvdrographs derived in this study.

Appendix B contains the unit hvdrographs derived for each event in the Wilsons catchment. Typically, the first couple of ordinates in the derived unit hvdrograph were negative whilst significant fluctuations occurred on the falling limb. Similar results were obtained for the Tweed and Macleay catchments.

A relatively simple, though somewhat arbitary method was employed to overcome these inconsistencies. A line of best fit was drawn through the calculated ordinates with the aim of maintaining the volume of the unit hydrograph.

TABLE 5.2 UNIT HYDROGRAPH PEAK TIMES

Time to peak of derived UH in hours

Event Tweed Wilsons Macleay

1 9.3 20 18 2 10.2 22 18 3 8.4 26 * 4 9.6 * 24 5 24 * 6 * * 27 7 8.4 26 * 8 * * 27 9 7.5 22 30 10 9.9 22 21 11 na 36 30 Median 9.3 23 24

* signifies test event

42 For each smoothed unit hydrograph, the time of the peak was abstracted and the median determined. Table 5.2 gives the time to peak for each flood in each catchment and indicates the variability that exists between the unit hydrographs derived from each event. Then each smoothed unit hydrograph was nested about the median and ordinates read off at each three hourly interval. After doing this for each event, the average unit hvdrograph for the catchment was calculated. These calculations for the

Wilsons River to Lismore are also given in Appendix B.

The unit hvdrographs derived for each catchment are tabulated in Table 5.3.

TABLE 5.3 THREE HOUR UNIT HYDROGRAPHS

Note: Ordinates in cubic metres per sec Time Tweed River Wilsons River Macleav River Period to to to (3 hr) Murwillurnbah Lismore Kempsev 1 2.5 0.5 5 2 9.1 1.4 12 3 13.1 2.6 19 4 10.7 4.6 30 5 8.0 7.3 43 6 5.3 9.5 62 7 3.6 10.7 80 8 2.2 11.0 87 9 1.4 10.3 83 10 0.9 9.3 76 11 0.6 8.4 67 12 0.4 7.5 60 13 6.8 53 14 6.1 46 15 5.5 40 16 4.8 35 17 4.2 30 18 3.7 26 19 3.2 23 20 2.8 20 21 2.5 17 22 2.1 15 23 1.9 11 24 1.7 7

43 5.1.3 NETWORK MODELS

The technique used to calibrate RORB and WBNM was similar. The process involved changing model parameters until a best fit was obtained between the calculated hvdrograph and the observed hydrograph.

Generally, best fit was defined as matching the rising limb of the hydrograph, the peak discharge and the timing of the peak. Of course, this could not be achieved exactly so the concept of best fit tends to be somewhat subjective.

In RORB, a'number of properties of the observed and calculated hvdrographs were calculated and compared.

These included the peak discharge, time to peak, hvdrograph volumes and average absolute ordinate error. This made the calibration process for RORB a little easier than for WBNM which did not have these facilities in the version used.

RORB and WBNM have two model parameters which can be varied to obtain the best fit. One is the main catchment parameter while the other is related to the degree of non-linearity of the model. In RORB, these are KC and m respectively and in WBNM, C and x. It is important to note that in both models the two parameters are interactive. It could be that there may be more than one set of calibration parameters for each flood event.

44 Weeks(1980) suggested the parameter indifference

method may overcome this problem when using RORB. A set of KC and m values giving a reasonable fit are determined for each flood and a curve of KC versus m plotted. This is

done for a number of floods and often the resulting curves

seem to intersect in a general area thereby defining

a unique set of model parameters. This procedure was

tried in calibrating RORB for the Tweed catchment. The

resulting indifference curve, Figure 5.1 , was

inconclusive and the method abandoned for the remainder of

the study.

FIGURE 5.1 TWEED RIVER - RORB PARAMETER INDIFFERENCE CURVES

45 The procedure adopted to calibrate the network models was to hold the non-linearity parameter constant and vary the other parameter, KC in RORB and C in WBNM, to achieve a fit. This process appears to be quite reasonable given the recommendations of the authors of the models. For RORB, it is recommended that m be held constant at 0.8 unless there are firm indications that it varies significantly from this value. Trial runs in the three catchments gave no such indications and a constant value of 0.8 was adopted for m. Similarly, with KBNM, it is recommended that in normal use the value of the non­ linearity parameter be held constant at the suggested value of -0.23.

TABLE 5.4 MODEL CALIBRATION PARAMETERS

(a) Tweed River to Murwillumbah

Event RORB WBNM KC C

1 32 1.9 2 31 1.8 3 35 1.9 4 28 1.6 5* - - 6 * - - 7 50 3.0 8 * - - 9 32 2.0. 10 39 2.3 Adopted 32 1.9

46 TABLE 5.4 (contd) MODEL CALIBRATION PARAMETERS

(b) Wilsons River to Lismore

Event RORB KC

1 94 2 86 3 62 4 * - 5 99 6 * - 7 91 8 * - 9 79 10 94 11 97

Adopted 94

(c) Macleay River to Kempsey

Event RORB WBNM KC C

1 210 2.1 2 180 1.8 3 * - - 4 180 1.6 5 * - - 6 210 1.9 7 * - - 8 260 2.0 9 200 1.5 10 180 1.8 11 230 2.2

Adopted 210 1.9

Thus for each network model, the main catchment parameter was the only parameter varied until a reasonable fit between observed, and calculated hydrographs was obtained. Table 5.4 shows the range and adopted values of the main model parameters in all three catchments and gives some indication of the variability of the parameters between individual events. The WBNM model was not used on

47 the Wilsons River.

Typical calibration runs of RORB and WBNM are given in

Appendix C for three events on the Macleav catchment. The fit obtained varied greatly from event to event and from catchment to catchment. Of the three events given for the

Macleav River, a reasonably good fit between observed and calculated hydrographs was obtained for events 1 and 2 but the fit for event 3 indicates up some inadequacies.

5.2 RESULTS

Each model was re-applied to each calibration flood in each catchment using the adopted model parameters derived in the calibration process. This part of the study was carried out in two steps. Initial losses and model calibration parameters were held constant in both steps but the continuing loss rate was altered.

In the first step, the models were applied to all the flood events, including the test events, using the initial loss estimated for that particular event with adopted values of continuing loss and model parameter. As the initial loss had not previously been derived for the test events, it was estimated during this step and used during the second step. The results of this first part of the study are contained in Appendix D in the Tables

D.l(a), D.2(a) and D.3(a) for the Tweed, WTilsons and Macleav catchments respectively.

48 In the second part, the initial loss and continuing loss estimated for the particular event was used in each model along with the adopted value of the model parameter.

The purpose of this step was to test the effect of the continuing loss as well as accuracy and consistency of the runoff model. The results of this step for each catchment are given in Tables D.l(b), D.2(b) and D.3(b).

For each flood event and for each model, the ratio of the modelled peak discharge to the actual peak discharge was determined. Additionally, the difference in timing between the modelled peak and actual peak in hours was computed. These values were then used as indicators of model performance.

TABLE 5.5 SUMMARY OF MODEL RESULTS

(a)* Initial loss as indicated for each event in Table 5.1 * Adopted continuing loss as shown at the bottom of Table 5.1

UH RORB WBXM Basin Qp (%) T (h) Qp (%) T (h) Qp (%) T (h) Tweed Ave 107 + 1.7 114 + 0.3 107 -1.0 SD 40 2.6 53 2.3 51 2.1 CC 0.71 0.71 0.68

Wilsons Ave 103 -3.0 73 + 1.5 — — SD 19 4.5 21 6.0 - - CC 0.91 0.91

Macleav Ave 99 + 1.2 95 -2.4 81 -2.4 SD 57 8.1 28 9.4 32 7.5 CC 0.55 0.76 0.75

49 TABLE 5.5 SUMMARY OF MODEL RESULTS (contd)

(b)* Initial and continuing losses as indicated for each event in Table 5.1

UH RORB WBNM Basin Q(%) T (h) Q(%> T (h) Q (%) T (h) Tweed Ave 104 + 1.7 109 -0.3 92 -0.3 SD 15 2.6 26 1.8 18 2.8 CC 0.96 0.92 0.89

Wilsons Ave 107 -3.0 78 + 1.5 — — SD 18 4.5 14 6.0 - - CC 0.95 0.98

Macleay Ave 110 + 2.1 94 -2.7 90 -2.1 SD 26 7.5 17 10.0 14 8.0 CC 0.87 0.83 0.84

* Qp(%) = Q(modelled peak) / Q(actual peak) in percent * T(h) = T(modelled peak) - T(actual peak) in hours * CC = correlation coefficient between actual and modelled peak discharges.

In each catchment and for each model, the average and standard deviations of the discharge ratios and the timing differences of each event were computed and are shown in Table 5.5. Additionally, Table 5.5 gives the correlation coefficients between actual peak discharges and modelled peak discharges.

The average value is considered to be an overall measure of the accuracy of each model as it represents the ability of each model to reproduce the actual flood peak.

The standard deviation and the correlation coefficient are considered to be estimates of the consistency of each model. A consistent model is taken to be one which exhibits the same trend over the range of the events.

50 6. DISCUSSION

6.1 Rainfall Distribution and Losses

As discussed in 3.6, the method of distributing rainfall and determining losses in each of the three models varied slightly. This resulted in slightly different calculated losses between those used for the unit hvdrograph and those used for the network models.

The effect was especially significant in the Macleay catchment. In the other two catchments there was no appreciable difference in the losses.

In the Macleay catchment, Table 5.1(c) shows that there is a marked difference between the losses determined for the unit hydrograph model and the network model. Generally both initial and continuing losses are higher for the network models. The reason appears to be related to the way in which rainfall is allocated in the models and the rainfall loss model applied.

In the unit hydrograph model, rainfall is distributed uniformly over the catchment and the way in which the rainfall loss model is applied supposes that runoff commences at the same time all over the catchment. On the other hand, the network models account for the spatial variability of the rainfall by allocating rainfall by sub- area but again there are problems with the application of the loss model. As used in this study and as normally applied, initial loss is assumed to be uniform over the catchment. This assumption means that runoff is supposed to commence at different times on different parts of the

51 catchment. While this supposition is probably true, the assumption that initial loss is uniform over the catchment is not.

It is quite likely that both initial and continuing losses vary spatially throughout the catchment and that runoff commences on different parts of the catchment at different times. In this respect RORB and WBNM model the physical runoff processes better than the unit hvdrograph.

The version of WBNM used in this study has the capacity to take the spatial variation of losses into account but to be able to use this facility requires much more data and research.

However, given these limitations of the models, the losses computed are generally within the ranges of losses found in other studies.

The continuing loss rate recommended in ARR(1987) for design purposes in these catchments is 2.5 millimetres per hour and Table 6.1 of that publication gives a list of median and average loss rates for a number of eastern coastal catchments. The continuing loss rates determined in this study fall within the ranges given in this Table.

Interestingly, the variation in the continuing loss rate was greatest in the smallest catchment, the Tweed and smallest in the largest catchment, the Macleay.

Initial losses, however, tend to be higher than those recommended for design purposes. There may be a number of reasons for this.

52 As mentioned in Chapter 3, the quality of the data is questionable in some events. It is suspected that in those events with particularly high initial losses that the first part of the hydrograph is missing whilst in those events with zero initial loss, some rainfall data was missing. Apart from these anomalies, the remaining initial losses appear to be reasonable.

6.2 Model Performance

The performance of each of the models in reproducing observed flood hydrographs varied from catchment to catchment and also under the loss rate assumptions.

Table 5.5(a) shows the results obtained when the models were run using the estimated initial losses and the adopted values of continuing loss and model parameter. Overall, the three models give reasonable estimates of the magnitude and timing of the peak flow in each catchment.

The test events in the Tweed catchment appeared to confirm that the adopted continuing loss rates and/or model parameters were reasonable values. Each of the three models were able to reproduce both the magnitude and timing of the peak flow in each of the three test events to within acceptable tolerances.

In the Tweed catchment, the ability of the unit hvdrograph to reproduce the magnitude of the flood peak averaged out over the 7 fit events to 103%. RORB and WBNM had averages of 114% and 107% respectively. Based on

53 these results, it is difficult to decide which model performs best.

Of the 7 fit events used in the Tweed catchment, two, events 7 and 10, were multi- peaked. In event 7 all three models grossly underestimated the second peak while in event 10 the reverse occurred with all three models overestimating the second flood peak. However, in both cases, the first flood peak was modelled with reasonable accuracy.

Overall it is considered that the unit hvdrograph gives a better estimate of the magnitude of the flood peak but RORB gives a better estimate of the timing of the peak. The unit hvdrograph, by virtue of its lower standard deviation and higher correlation coefficient, is considered to be a little more consistent than the network models in the Tweed catchment.

Unlike in the Tweed catchment, the test events in the

Wilsons catchment were unable to confirm or deny that the adopted continuing loss rates and/or model parameters were typical values. Whilst some indication of the correctness of the model parameter might be inferred from the ability of each model to reproduce the timing of the flood peak, the lack of their ability to model the magnitude of the peak only served to confirm a suspicion that developed during the study, ie that the loss model was more important than the runoff model.

In the Wilsons catchment, the ability of the unit hvdrograph to reproduce the magnitude of the flood peak,

54 ranged from 67% to 179% with an overall average of 103% while RORB had a range from 46% to 138% with an overall average of 73%. During the calibration, RORB consistently underestimated the flood peak but otherwise gave reasonable fit with the time of the peak and the shape of the actual runoff hvdrograph. Therefore the overall under-estimating of the flood peak is not unexpected.

The unit hydrograph model for the Wilsons River was able to model the timing of the flood peak generally within 6 hours with an average of 3 hours early in the 8 events tested. RORB, whilst being overall more accurate with an average of 1.5 hours late, exhibited a much wider range of timing differences than the unit hydrograph.

On overall performance, the unit hvdrograph is considered to be superior to RORB in modelling floods in the Wilsons catchment.

The three test events in the Macleav catchment did not serve to substantiate the adopted continuing loss rate and model parameter. Reasonable reproduction of the observed hvdrograph was obtained in events 3 and 5 but event 7 highlighted the need for an accurate estimate of excess rain.

Both network models gave better overall results than the unit hvdrograph in the Macleav catchment. While, on average, the unit hvdrograph reproduced the magnitude of the flood peak marginally better, it was not as consistent

55 as RORB or WBNM. Both RORB and WBNM had markedly better standard deviation and correlation coefficients.

However, the reproduction of the timing of the flood peaks in the Macleav was generally poor. Again while the unit hvdrograph was most accurate, both WBNM and RORB were more consistent. The poor timing performance may indicate that there are errors in the original data.

There were two multi-peaked events used in fitting the model to the Macleav catchment, events 4 and 6. In both of these events, the models did not seem to be able to reproduce the second peak or subsequent peaks. There would appear to be two explanations, either there are errors in the rainfall data or secondly, the IL-CL type of loss model does not apply to multi-peaked events. It is suspected that during second and subsequent rain bursts that the continuing loss may be much less than during the initial rainfall.

Overall as the network models appear to be more consistent, they are preferred.

Generally, there is a marked improvement in the performance of all three models between Table 5.5(a) and

5.5(b) where estimated losses were used in conjunction with adopted model parameters. This, of course, is expected since actual excess rainfalls are modelled instead of estimated values . Figure 6.1 shows the difference between the two steps for an event in the Tweed catchment. This improvement was typical in events in all three catchments.

56 Tueed River to Muruillurnbah Event No 2 Actual IL, adopted CL & model parameter

UBNM RORB UH Observed

Tueed R1 ve r t o I lu r u 111 umbah Event No 2 Actual IL & CL, adopted model parameter Discharge (rno/s)

-----CIBNLI ...... RORB - ....UH — Observed 8 10 1 14 16 18 20 22 24

Time Periods (x 3 Hours)

COMPILED DRAWN BASIN No. T am TWEED RIVER FIGURE DATE DRAWN DATE AMENDED MODEL RESULTS 6-1 57 There are significant improvements in averages, standard deviation and correlation coefficients indicating how much better each model could perform if excess rainfall can be estimated accurately.

As in the first step, the unit hydrograph tends to be as good, if not better, than RORB and WBNM in modelling the magnitude of the flood peaks in the Tweed catchment.

RORB maintains its position as being best able to reproduce the timing of the.peak.

In the Wilsons catchment, the improvement in the performance of each model is not as significant as in the Tweed and varies between the two models used. There is little improvement in the performance of the unit hydrograph but a more significant improvement in the performance of RORB. The relative smallness of this improvement is not surprising as the variation in the loss rates calculated for each events is not great.

Similarly to the results in the Wilsons catchment, there are not great improvements in the Macleav catchment to the overall performance of each model. Again this appears to be related to the relatively small variation in the continuing loss rate from event to event. There are, however, marked improvements in the consistency of each model with the network models maintaining their superiority ovre the unit hydrpgraph in this catchment.

58 It would appear that in all three catchments, an accurate estimate of rainfall losses is more critical than the type of runoff model used to determine the direct runoff hvdrograph.

6.3 General Discussion

Even though the results of the study do not explicitly show it, it is considered that network models offer a number of advantages over unit hvdrographs for flood forecasting.

Network models would allow forecasts to be made for any number of locations in a catchment using only one model provided they have been previously calibrated at these locations. On the other hand, a number of separate unit hydrographs would be required to achieve the same result. For example, in the Macleav catchment, forecasts are required for Georges Creek and Bellbrook, both upstream of Kempsev. Usually three separate unit hvdrographs are run during flood forecasting operations but the same information could be obatined using one network model. Additionally, RORB and WBNM have reservoir routing modules which mean that one model could be used for many different conditions whereas these facilities are external to the unit hydrograph. From these aspects, network models would simplfy flood forecasting operations by reducing the number of models required in each catchment to one.

As the network models were more consistent in the

59 largest catchment, it is suggested that they better model the spatial and temporal variation of rainfall which occurs in this catchment. Network models also have the potential to model the spatial variation of losses which is certain to occur on large catchments although more research in this field is required to define this potential.

It is quite likely that the larger the catchment the more significant the effect of the spatial variation of rainfall and non-linearity of catchment response. This may be one reason that the use of unit hydrograph is generally restricted to catchments with areas less than 5000 square kilometres. Network models can account for catchment non-linearity in a more integrated manner than unit hydrographs. Whilst there are methods which allow for adjustment to the peak flow calculated by the unit hvdrograph to take account of non-linearity (Body 1962), they are somewhat empirical and are external to the model itself. The problem with network models is not in the question of linearity but in the form in which the non­ linearity is modelled (ARR 1987). The power relation used in the RORB and WBNM models (Eqns 4.1, 4.3) may not be definitive though evidence seems to indicate a relationship of this form.

Network models make more explicit use of available information. Measureable catchment data such as area, stream length, slope, percentage imperviousness, soil infiltration capacity etc, might be used explicitly in a network model whereas such information is lumped in the

60 unit hydrograph model and their effect is masked to the user. Because of this property, network models have a better ability to model changes in some catchment characteristics.

Any number of rainfall stations can be used in the network model. Body & Hall (1978) showed that four to six stations are usually sufficient to define catchment average rainfall for unit hydrographs and the use of more stations does not improve the accuracy of flood estimation using a unit hvdrograph. Many more rainfall stations can be used in the network model with perhaps ideally each sub-area having its own rainfall station.

Another advantage of the network model is that it can be recalibrated during a flood event if necessary. As shown in Table 5.4, there can be a significant variation in the model parameters between events both in the unit hydrograph and the network models. The calibration of the network model can be readily altered to suit any observed catchment responses.

61 7. CONCLUSIONS AND RECOMMENDATIONS

The aim of this study was to determine if two network models, RORB and WBNM, could give more accurate and consistent results than the unit hvdrograph which is currently the most commonly used model for flood forecasting.

In all three catchments investigated, there appears to be little difference in the ability of the unit hydrograph and the network models used in this study to reproduce observed flood hvdrographs. This is certainly the case in the Tweed and Wilsons catchments with perhaps the unit hvdrograph being marginly superior. It is in the largest of the three catchments, the Macleay that both network models, RORB and WBNM appear to give slightly more consistent results.

However, it appears that the rainfall loss model is more critical than the runoff model. In all three catchments, the performance of each runoff model was considerably improved by a more accurate estimate of the continuing loss rate. While the overall average performance of each model was not significantly changed by using actual continuing loss rates, their use did result in a greater consistency.

Each of the models used in the study had some limitation with distribution of rainfall and application of the IL-CL loss model. Obviously if the accuracy of flood forecasting and indeed general catchment modelling is to improve, better methods of estimating the

62 distribution of excess rainfall on large catchments will need to be addressed.

The study also served to emphasise the need for accurate and reliable rainfall and flow data. It would appear that accurate data is more important than the level of sophistication of the runoff model. As the calibration of rainfall-runoff models is largely dependent upon ratings at particular locations, it would be highly desirable to - see improvements in their quality.

Network models offer a number of advantages over unit hvdrographs for flood forecasting especially in larger catchments. They have the ability to model the spatial variation in rainfall which is commonly a defect in unit hydrographs during storms with heavy localised rainfalls. Additionally, they have the potential to model the variation in loss parameters and may be part of the answer to the problem of spatial non-homogenietv. Network models address the problem of catchment non-linearity although the.actual relationship is still subject to .more research. They also offer a degree of flexibility to the forecaster over the unit hydrograph to alter model parameters during operational use.

63 REFERENCES

Body, D. N. (1962) Significance of peak runoff intensity in the application of the uni t graph method to flood estimation. Journal of Institution of Engineers,

Australia, Vol. 34.

Body, D. N. & Hall, A. J. (1978) Case study of a rainfall reporting network for flood forecasting in the Macleav

River, Australia. Casebook of Hydrological Network Design.

WMO No. 168, Supplement No. 1, Geneva.

Boyd, M. J., Pilgrim, D. H. and Corderv, I. (1979) A watershed bounded network model for flood estimation - computer program and users guide. Water Research Lab, Uni of NSW, Report No 154.

Boyd, M. J. ( 1983 ) A comparison of the RORB & WBNM storage routing models. Uni of Wollongong, Research Report WE/83/1.

Boyd, M. J. (1985) Effect of catchment sub-divison on runoff routing models. Civ. Engg Trans., Inst. Engrs Aust., Vol. CE 27.

Bureau of Meteorology (1983) Bureau of Meteorology Flood

Forecasting and Warning Service 1983 Bureau of

Meteorology Dept of Science and Technology.

Hall, A. J. (1972) Methods of selection of areal rainfall stations and the calculation of areal rainfall for flood forecasting purposes. Bureau of Meteorology, Working

Paper 146. Institution of Engineers, Australia (1987) Australian rainfall and runoff.

Kneen, T. & Graham, G. S. (1977) Runoff routing and its application in flood forecasting models. Internal

Unpublished Report, Bureau of Meteorology.

Klassen, B. and Pilgrim, D.H. (1975) Hydrograph recession constants for New South Wales streams. Civ. Eng. Trans.,

Inst. Engrs Aust, Vol. CE17.

Laurenson, E. M. (1964) A catchment storage model for runoff routing. Journal of Hydrology, Vol 2.

Laurenson, E. M. & Mein, R. G. (1985) RORB - Version 3

Runoff routing program - User manual. Australian Computer

Aided Design Society, 2nd Ed.

Laurenson, E. M. & Mein, R. G. (1975) Comparison of unit hydrograph & runoff routing methods of flood estimation.

Institution of Engineers, Australia, Hydrology Symposium.

Public Works Dept of NSW (1980) Macleay Valley Vol 1. NSW

Coastal Rivers Flood Plain Management Studies.

Public Works Dept of NSW (1980) Richmond Valley. NSW

Coastal Rivers Flood Plain Management Studies.

Public Works Dept of NSW (1980) Tweed Valley. NSW Coastal

Rivers Flood Plain Management Studies Public Works.

Public Works Dept of NSW (1980) Lismore Floodplain

Management Study. World Meteorological Organization (1975) Hydrological forecasting practices, Operational hydrology report No. 6. World Meteorological Organization. APPENDIX A

RATING TABLES

STATION NUMBER 2 0 3 00 4 RATING TABLE NUMBER : N/A DATE TABLE ENTERED ON FILE, FLOODATA.RATETABF : 1 2 /0 1r- /0 \~ rr CO o C£T co C5 UJ UJ CC UJ COi ro

• :%

uo X c? o £ —i < _J

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00

o O 00 O CO CO oo 0' O O' bO U0 c0 co r~ UO o oo •

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oo r- CO o o oo o o ■=t o in o o O o in oo rr o

1 G 0 0 1 G3 0 1GS0 1710 17G0 1700 1030 10 70 1010 10G

APPENDIX B

WILSONS RIVER TO LISMORE

UNIT HYDROGRAPH DERIVATION LSorO S TO U 5 M (Z£: O “ ,

:..

-.i * * T-"TT-rr'OTTrrr- J'T

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( 3 h ) WILSONS RIVER TO LISMORE

UNIT HYDROGRAPH

AVERAGE TIME TO PEAK

Event Time to Peak (Hours)

1 20 2 22 3 26 5 24 7 26 9 22 10 22 11 27

Average 24 Median 23 _

Adopt 7.7 periods, ie 23 hours, as the time to peak for typical unit hvdrograph for the Wilsons River to Lismore. WILSONS RIVER TO LISMORE

AVERAGE UNIT HYDROGRAPH

Event Period Average 1 2 3 5 7 9 10 11 {m3/s)

0 0 0 0 0 0 0 0 0 0 1 0 0.4 0.8 0.5 0.7 0.4 0.4 0.8 0.5 2 1.2 1.3 1.7 1.1 1.5 1.2 1.4 1.4 1.4 3 2.8 2.6 3.3 2.1 2.8 2.3 2.6 2.3 2.6 4 4.7 4.0 6.0 3.7 6.1 4.1 4.4 3.6 4.6 5 7.1 6.1 11.1 6.0 9.0 6.8 6.6 5.7 7.3 6 9.6 9.6 13.3 7.9 10.2 8.2 9.2 7.9 9.5 7 11.0 11.3 14.5 8.8 10.8 8.7 11.7 8.8 10.7 8 11.3 11.6 14.6 9.0 11.1 8.8 12.6 9.2 11.0 9 10.4 10.7 13.7 8.7 10.6 8.6 11.0 9.0 10.3 10 8.7 9.6 11.9 8.5 9.8 8.1 9.2 8.6 9.3 11 7.4 8.6 10.3 8.1 9.0 7.6 8.0 7.9 8.4 12 6.5 7.8 8.7 7.7 8.3 7.1 6.9 7.3 7.5 13 6.0 7.0 6.9 7.2 7.5 6.7 6.1 6.7 6.8 14 5.4 6.3 5.4 6.7 6.8 6.3 5.5 6.2 6.1 15 5.0 5.7 4.0 6.3 6.1 6.0 5.1 5.6 5.5 16 4.6 5.0 2.6 5.8 5.3 5.6 4.6 5.0 4.8 17 4.2 4.5 1.4 5.4 4.5 5.2 4.1 4.5 4.2 18 3.9 3.9 0.4 4.8 3.8 4.7 3.7 4.2 3.7 19 3.5 3.4 0 4.4 3.2 4.2 3.3 3.8 3.2 20 3.2 2.8 0 3.8 2.8 3.8 2.9 3.4 2.8 21 3.0 2.4 0 3.4 2.3 3.4 2.5 3.0 2.5 22 2.7 2.0 0 2.9 1.8 3.0 2.1 2.6 2.1 23 2.5 1.7 0 2.5 1.6 2.6 1.8 2.3 1.9 24 2.4 1.5 0 2.1 1.4 2.2 1.5 2.1 1.7 Sum of Ordinates 128.4

Volume check = ( 128.4 x 3 x 3600) / 1400

0.99 mm Wilsons River to Lismore

Period UH Ordinate (3 hr) (m3/s) 0.5 1.4 2.6 4.6 7.3 9.5 10.7 11.0 10.3 9.3 8.4 7.5 6.8 6.1 5.5 4.8 4.2 3.7 3.2 2.8 2.5 2.1 1.9 1.7

TIME PERIODS

COMPILED DRAWN BASIN No. 203 "TAM WILSONS RIVER TO LISMORE FIGURE DATE DRAWN DATE AMENDED 3hr UH APPENDIX C

MACLEAY RIVER TO KEMPSEY

TYPICAL RORB & WBNM CALIBRATIONS MACLEAY RIVER TO KEMPSEY

EVENT NO. 1 VERSION 3.7 C, 21Aug87), COPYRIGHT MONASH UNIVERSITY

•THIS COPY SUPPLIED TO : Bureau of Meteorology 02Dec87 pATA FROM FILE :20640201.DAT • OUTPUT TYPE 1 pATA CHECK COMPLETED

INPUT OF PARAMETERS: ********************

macleay river to KEMPSEY fit RUN | INITIAL TIME: 0900 11TH JUNE 1967 TIME INCREMENT = 3.00 HOURS ( \ ; 3S MODEL 1 SELECTED

RUN 1 INITIAL LOSS = 20.0 MM CONTINUING LOSS RATE = 2.16 MM/H

ROUTING RESULTS: **************** , MACLEAY RIVER TO KEMPSEY 1 INITIAL TIME: 0900 11TH JUNE 1967 FIT RUN NO. 1

, PARAMETERS: KC= 210.00 M= .80 1 LOSS PARAMETERS: INITIAL LOSS (MM) CONT. LOSS (MM/H) 20.0 2.16

*** GAUGING STATION AT: KEMPSEY

HYDROGRAPH ERROR CALC. ACTUAL ABS. PERCENT PEAK DISCHARGE,M~3/S 4033. 3670. 363. 9.9 TIME TO PEAK,H 66.0 66.0 .0 .0 VOLUME,M~3 7.40E+08 7.63E+08-2.23E+07 -2.9 AV.ABS.ORD.ERR,M~ 3/S 140.5 10.1 OVER DUR. OF CALCS TIME TO CENTROID,H 76.1 75.6 .4 .6 LAG (C.M. TO C.M.),H 36.5 36.1 .4 1.2 LAG TO PEAK,H 26.5 26.5 .0 .0 i£IME DISCHARGE DISCHARGE, M~3/S X: CALC. O: ACTUAL CALC . ACTUAL 0 807. 1613. 2420. 3226. 4033. JNCS. M~3/S M~3/S I...... I...... I * 5 R/FALL 10 EXCESS 15 MM 20 25 0 0. 0. * 1 0. 0. * 2 0. 0. a 3 0. 0. a 4 0. 0. a - 5 0. 0. * 6 0. 0. * 7 0. 0. a 8 0. 0. a 9 9. 30. * 10 39. 60. *0 ------11 142. 220. * xo 1 1 1 1 1 * 0 12 376. 545. X X 0 * 13 748. 840. 1 1 1 14 1208. 1760. * — x O 15 1729. 2440. * X O 16 2239. 2750. A — X O 17 2706. 2910. * --- X O 18 3155. 3090. * -- OX \9 3534. 3280. * -- O X 20 3811. 3480. A — \ o X 21 3970. 3570. A - 0 X 22 4033. 3670. A-- O X 23 3994. 3670. A — O X 24 3867. 3670. A - O X 25 3670. 3620. A ox 26 3426. 3480. A xo 27 3150. 3230. rt xo 28 2856. 3000. A X 0 29 2556. 2710. A X 0 30 2266. 2440. A X 0 31 1996. 2210. A X 0 32 1751. 1950. A X 0 33 1532. 1600. * XO 34 1338 . 1400. * O 35 1169. 1240. * XO 36 1022. 1150. * xo 37 894. 1040. * X 0 X 38 783. 970. •K o 39 687 . 860. * X 0 40 604. 750. * X 0 41 532. 640. * xo 42 470. 570. * xo 43 416. 465. * xo 44 369. 370. * 0 45 328. 300. * 0 46 292. 230. * ox 47 260. 180. * ox 48 233. 130. * ox 49 209. 70. *0 X 50 . 187. 30. A X I...... I...... I...... I...... I...... I

0 807. 1613. 2420. 3226. 4033.

FINISHED MAX. REAL ARRAY STORAGE = 2965 WORDS MAX. integer ARRAY STORAGE = 396 WORDS max. character ARRAY STORAGE^ 104 words \fjb N M • SUMMARY OF CATCHMENT DATA

MACLEAY RIVER TO KEMPSEY NUMBER OF SUB-AREAS= 46 NUMBER OF BRANCHES^ 3

START AND END SUB-AREAS OF EACH BRANCH IN TURN 57 13 19 21 29 SUB-AREA CODES: 10 10 1 10 0 1 0 10 11 0 10 1 0 0 110 0 1 0 1 0 0 0 10 10 10 10 1 0 10 1 0 10

SIZES OF SUB-AREAS (HECTARES): 18300.0 22700.0 46500.0 19300.0 23300.0 47000.0 28100.0 0.0 29100.0 9000.0 43200.0 0.0 39000.0 32400.0 13100.0 27200.0 0.0 29500.0 0.0 15600.0 24300.0 24000.0 30400.0 28800.0 32400.0 16000.0 45200.0 36100.0 31100.0 9000.0 36100.0 24600.0 16000.0 44900.0 20500.0 0.0 26600.0 19300.0 21400.0 23300.0 35000.0 0.0 13400.0 27200.0 24200.0 7000.0 SUMMARY OF PARAMETER VALUES

0900 11TH JUNE 1967

PARAMETER C: 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10

NONLINEARITY PARAMETER : 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23

.iCTORS FOR INTERBASIN STREAM SEGMENTS: 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 SUMMARY OF STORM LOSSES

INITIAL LOSS (MM) « 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00

LOSS RATE (MM/PERIOD): 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 ft so ft ftn ft ftn ft . ftn ft . BO 6.50 rflME PERIOD (HOURS) = 3.00

depth EXCESS RAIN (MM) = 69.74

depth CALC. HYDROGRAPH (MM) = 69.59 CALC. PEAK DISCHARGE (M3/S) = 3639.05 CALC . TIME TO PEAK (HOURS) = 63.00 calc . HYDROGRAPH DELAYED (HOUR) = 0.00

RECD PEAK DISCHARGE (M3/S) = 3670.00 RECD TIME TO PEAK (HOURS) = 66.00

RAINFALL DEPTHS (MM): 27 69 58 248 308 337 149 TIME CALCULATED RECORDED RAINFALL HYETOGRAPH HOUR M3/S M3/S MM/PERIOD 0.00 0.00 0.00 * * * * * * 3.00 0.00 0.00 0 1 0 9 3 6 2 6.00 0.00 0.00 0 1 0 9 3 6 2 9.00 0.00 0.00 0 1 0 9 3 6 2 12.00 0.00 0.00 ' 0 2 1 9 3 7 2 "5.00 0.00 0.00 0 2 1 9 4 7 3 1.8.00 0.01 0.00 0 2 1 9 4 7 3 21.00 0.08 0.00 1 2 1 9 4 7 3 24.00 0.28 0.00 1 2 1 9 4 7 3 27.00 19.66 - 30.00 1 2 2 18 25 28 11 30.00 102.85 60.00 1 5 3 30 27 25 11 33.00 331.63 220.00 2 6 3 12 27 29 18 36.00 716.17 545.00 1 4 3 9 28 30 13 39.00 1186.52 840.00 2 7 4 11 19 15 11 42.00 1615.80 1760.00 1 4 3 10 13 15 3 45.00 1997.16 2440.00 2 1 4 11 10 6 15 48.00 2332.80 2750.00 3 3 6 14 20 32 4 51.00 2724.97 2910.00 4 5 6 15 28 22 13 54.00 3101.71 3090.00 6 11 9 13 17 17 8 57.00 3385.31 3280.00 0 1 4 12 16 18 6 60.00 3567.83 3480.00 1 3 1 7 15 13 4 63.00 3639.05 3570.00 0 1 2 7 11 9 5 66.00 3611.60 3670.00 0 2 1 5 13 12 1 69.00 3512.93 3670.00 0 1 1 2 3 3 2 2.00 3358.56 3670.00 1 0 1 0 8 10 4 / 5.00 3163.03 3620.00 0 0 0 0 0 0 0 78.00 2931.76 3480.00 0 0 0 0 0 0 0 81.00 2672.09 3230.00 0 0 0 0 0 0 0 84.00 2413.45 3000.00 0 0 0 0 0 0 0 87.00 2164.51 2710.00 0 0 0 0 0 0 0 90.00 1932.05 2440.00 0 0 0 0 0 0 0 93.00 1719.58 2210.00 0 0 0 0 0 0 0 96.00 1528.26 1950.00 0 0 0 0 0 0 0 99.00 1357.77 1600.00 0 0 0 0 0 0 0 102.00 1206.88 1400.00 0 0 0 0 0 0 0 105.00 1073.95 1240.00 0 0 0 0 0 0 0 108.00 957.17 1150.00 0 0 0 0 0 0 0 111.00 854.70 1040.00 0 0 0 0 0 0 0 114.00 764.82 970.00 0 0 0 0 0 0 0 117.00 685.95 860.00 0 0 0 0 0 0 0 120.00 616.65 750:00 0 0 0 0 0 0 0 123.00 555.68 640.00 0 0 0 0 0 0 0 126.00 501.93 570.00 0 0 0 0 0 0 0 129.00 454.46 465.00 0 0 0 0 0 0 0 132.00 412.42 370.00 0 0 0 0 0 0 0 135.00 375.13 300.00 0 0 0 0 0 0 0 138.00 341.95 230.00 0 0 0 0 0 0 0 141.00 312.37 180.00 0 0 0 0 0 0 0 144.00 285.93 130.00 0 0 0 0 0 0 0 ___ Q___n n n n n n ID CU > z: CD CD z CD in CD □ _o IB CD o Hours)

S

Cx

PERIODS

TIME

CD CD CH m CD cn CD1—1 I i 1 i i i i I i i i i 1 i i i I I i i i i o o CD CD CD o o CD CD CD o CD CD m C\J t—i MACLEAY RIVER TO KEMPSEY

EVENT NO. 2 rQRB VERSION 3.7 C, 21Aug87), COPYRIGHT MONASH UNIVERSITY

THIS COPY SUPPLIED TO : Bureau of Meteorology 02Dec87 DATA FROM FILE :20640202.DAT OUTPUT TYPE 1 DATA CHECK COMPLETED

INPUT OF PARAMETERS: ********************

MACLEAY river to kempsey FIT RUN INITIAL TIME: 0900 11TH JANUARY 1968 TIME INCREMENT = 3.00 HOURS

i. SS MODEL 1 SELECTED

RUN 1 INITIAL LOSS = 80.0 MM CONTINUING LOSS RATE = 3.30 MM/H

ROUTING RESULTS: **************** MACLEAY RIVER TO KEMPSEY INITIAL TIME: 0900 11TH JANUARY 1968 FIT RUN NO. 1

PARAMETERS: KC= 180.00 M= .80 LOSS PARAMETERS: INITIAL LOSS (MM) CONT. LOSS (MM/H) 80.0 3.30

*** GAUGING STATION AT: KEMPSEY

HYDROGRAPH ERROR CALC. ACTUAL ABS. PERCENT PEAK DISCHARGE,M~3/S 3208. 3130. 78. 2.5 TIME TO PEAK,H 54.0 51.0 3.0 5.9 VOLUME,M~3 4.26E+08 4.34E+08-8 11E+06 -1.9 AV .ABS.ORD.ERR,M~3/S 246.6 25.2 OVER DUR. OF TIME TO CENTROID,H 66.5 64.2 2.3 3.6 LAG (C.M. TO C.M.),H 28.2 25.8 2.3 9.0 lag to peak,h 15.7 12.7 3.0 23.7 -time DISCHARGE DISCHARGE, M~3/S X: CALC O: ACTUAL CALC . ACTUAL 0 642. 1283. 1925. 2566. 3208. INCS. M~3/S M~3/S I...... I...... I...... I ..... I...... I * 5 R/FALL 10 EXCESS 15 MM 20 25 0 0. 0. * 1 0. 0. * 2 0. 0. * 3 0. 0. * 4 0. 0. * 5 0. 0. * 6 0. 0. * 7 0. 0. * 8 0. 0. * 9 16. 0. * - 10 80. 0. *X------11 162. 0. * x ------12 485. 75. *0 X ------13 1193. 300. * 0 ------X----- 14 1728 . 970. * 0 ----- X 15 1916. 2310. *------— x 16 2256. 3100. * O 17 2848. 3130. * X 0 18 3208 . 3120. rt OX 19 3158. 3000. * O X 20 2910. 2950. XO 21 2590. 2940. * X 0 22 2246. 2930. * X 0 23 1917. 2830. * * X 0 24 1626. 2610. * X O 25 1384. 2130. * X O 26 1190. 1810. * X 0 27 1035. 1790. * X 0 28 911. 960. * XO 29 807. 810. * 0 30 718. 640. * ox 31 639. 460. * ox 32 568. 390. * ox 33 504. 270. * O X 34 446. 190. * O X 35 394. 160. * O X 36 347. 130. * O X 37 305. 90. *0 X 38 269. 60. *0 X 39 237. 40. *0 X 40 209. 0. * X 41 184. 0. * X 42 163. 0. * X ■ 43 144. 0. * X 44 128. 0. * X 45 114. 0. * X 46 101. 0. * X 47 90. 0. *x 48 81. 0. *x 49 73. 0. *x 50 65. 0. *x I...... I

0 642. 1283. 1925. 2566. 3208.

FINISHED MAX. REAL ARRAY STORAGE = 2234 WORDS MAX. INTEGER ARRAY STORAGE = 396 WORDS MAX. CHARACTER ARRAY STORAGE^ 104 WORDS SUMMARY OF CATCHMENT DATA

MACLEAY RIVER TO KEMPSEY

NUMBER OF SUB-AREAS= 46 NUMBER OF BRANCHES= 3

START AND END SUB- AREAS OF EACH BRANCH IN TURN 5 7 13 19 21 29 SUB-AREA CODES: 1 0 1 0 1 10 0 1 0 10 110 1 0 10 0 110 0 1 0 1 0 0 0 10 10 10 1 0 10 1 0 10 1 0

SIZES OF SUB-AREAS (HECTARES): 18300.0 22700.0 46500 .0 19300.0 23300.0 47000.0 28100.0 0.0 29100.0 9000.0 43200 .0 0.0 39000.0 32400.0 13100.0 27200.0 0.0 29500.0 0 .0 15600.0 24300.0 24000.0 30400.0 28800.0 32400.0 16000.0 45200 .0 36100.0 31100.0 9000.0 36100.0 24600.0 16000.0 44900.0 20500 .0 0.0 26600.0 19300.0 21400.0 23300.0 35000.0 0.0 13400 .0 27200.0 24200.0 7000.0 SUMMARY OF PARAMETER VALUES

0900 11TH JANUARY’ 1968

PARAMETER C: 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80

NONLINEARITY PARAMETER : 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 wXTORS FOR INTERBASIN STREAM SEGMENTS: 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 SUMMARY OF STORM LOSSES

INITIAL LOSS (MM) • 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00

LOSS RATE (MM/PERIOD): 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 9.90 __g qd____q qn q qn q qn q qo q.qn IME PERIOD (HOURS) 3.00 [DEPTH EXCESS RAIN (MM) 41.21 DEPTH CALC. HYDROGRAPH (MM) 41.22 CALC. PEAK DISCHARGE (M3/S) 3001.52 CALC. TIME TO PEAK (HOURS) 51.00 CALC. HYDROGRAPH DELAYED (HOUR)= 0.00

RECD PEAK DISCHARGE (M3/S) 3130.00 RECD TIME TO PEAK (HOURS) 51.00

RAINFALL DEPTHS (MM) : 119 78 100 144 237 259 257 TIME CALCULATED RECORDED RAINFALL HYETOGRAPH HOUR M3/S M3/S MM/PERIOD 0.00 0.00 0.00 * * * A * * 3.00 0.00 0.00 10 1 4 4 8 5 8 6.00 0.00 0.00 10 1 4 4 8 9 8 9.00 0.00 0.00 10 2 4 4 8 5 8 12.00 0.00 0.00 10 2 4 4 9 7 8 ■’5.00 0.00 0.00 10 2 5 4 9 12 8 ^8.00 0.00 0.00 10 2 5 4 9 3 9 21.00 0.00 0.00 10 2 5 6 9 2 9 24.00 0.00 0.00 10 2 5 6 9 3 9 27.00 10.34 0.00 2 5 2 5 20 9 30 30.00 37.00 0.00 6 2 4 3 2 7 21 33.00 67.87 0.00 4 5 15 5 35 30 13 36.00 462.51 74.00 11 5 24 19 21 37 66 39.00 1086.56 300.00 8 17 5 25 14 26 53 42.00 1620.24 970.00 2 15 4 19 30 76 6 45.00 2273.45 2310.00 5 11 7 28 40 25 1 48.00 2813.89 3100.00 1 4 3 4 6 3 0 51.00 3001.52 3130.00 0 0 0 0 0 0 0 54.00 2927.92 3120.00 0 0 0 0 0 0 0 57.00 2725.41 3000.00 0 0 0 0 0 0 0 60.00 2470.42 2950.00 0 0 0 0 0 0 0 63.00 2216.79 2940.00 0 0 0 0 0 0 0 66.00 1980.38 2930.00 0 0 0 0 0 0 0 69.00 1766.00 2830.00 0 0 0 0 0 0 0 2.00 1572.56 2610.00 0 0 0 0 0 0 0 / 5.00 1397.91 2130.00 0 0 0 0 0 0 0 78.00 1240.40 1810.00 0 0 0 0 0 0 0 81.00 1098.89 1790.00 0 0 0 0 0 0 0 84.00 972.46 960.00 0 0 0 0 0 0 0 87.00 860.17 810.00 0 0 0 0 0 0 0 90.00 760.95 640.00 0 0 0 0 0 0 0 93.00 673.65 460.00 0 0 0 0 0 0 0 96.00 597.07 390.00 0 0 0 0 0 0 0 99.00 530.03 270.00 0 0 0 0 0 0 0 102.00 471.38 190.00 0 0 0 0 0 0 0 105.00 420.09 160.00 0 0 0 0 0 0 0 108.00 375.21 130.00 0 0 0 0 0 0 0 111.00 335.89 90.00 0 0 0 0 0 0 0 114.00 301.40 60.00 0 0 0 0 0 0 0 117.00 271.09 40.00 0 0 0 0 0 0 0 120.00 244.40 0.00 0 0 0 0 0 0 0 123.00 220.85 0.00 0 0 0 0 0 0 0 126.00 200.03 0.00 0 0 0 0 0 0 0 129.00 181.57 0.00 0 0 0 0 0 0 0 132.00 165.18 0.00 0 0 0 0 0 0 0 135.00 150.58 0.00 0 0 0 0 0 0 0 138.00 137.56 0.00 0 0 0 0 0 0 0 141.00 125.92 0.00 0 0 0 0 0 0 0 144.00 115.48 0.00 0 0 0 0 0 0 0 1 A n A A 1 r\ c ^ r\ ______a on a a A AAA A i~i a) >

m cu cn m m 0 _Q 13 cn f 1 Hours)

3

(x

PERIODS

TIME

LU CD QC cnm CD cn \—i cd a O a CD a a CD CD C_J CD 0 a XT' m C\J MACLEAY RIVER TO KEMPSEY

EVENT NO. 6 rORB VERSION 3.7 C, 21Aug87), COPYRIGHT MONASH UNIVERSITY

IHIS COPY SUPPLIED TO : Bureau of Meteorology 02Dec87 DATA FROM FILE :20640206.DAT OUTPUT TYPE 1 DATA CHECK COMPLETED

INPUT OF PARAMETERS: ********************

MACLEAY RIVER TO KEMPSEY FIT RUN INITIAL TIME: 0900 10TH NOVEMBER 1975 TIME INCREMENT =3.00 HOURS

iu SS MODEL 1 SELECTED

RUN 1 INITIAL LOSS = 170.0 MM CONTINUING LOSS RATE = .68 MM/H

ROUTING RESULTS: **************** MACLEAY RIVER TO KEMPSEY INITIAL TIME: 0900 10TH NOVEMBER 1975 FIT RUN NO. 1 PARAMETERS: KC= 210.00 M= .80 LOSS PARAMETERS: INITIAL LOSS (MM) CONT. LOSS (MM/H) 170.0 .68

*** GAUGING STATION AT: KEMPSEY

HYDROGRAPH ERROR CALC ACTUAL ABS. PERCENT PEAK DISCHARGE,M~3/S 1963. 2340. -377. -16.1 TIME TO PEAK,H 114.0 114.0 .0 VOLUME,M~3 12E+08 50E+08-3.78E+07 -5 AV.ABS.ORD.ERR,M~3/S 205.3 20 OVER DUR. OF CALCS TIME TO CENTROID,H 96.7 96.3 .4 LAG (C.M. TO C.M.),H 33.2 32.7 .4 LAG TO PEAK,H 50.5 50.5 .0 ±i\u.= j.uu n fXME DISCHARGE DISCHARGE, M~3/S X: CALC. O: ACTUAL CALC . ACTUAL 0 468. 936. 1404. 1872. 2340. [NCS. M~3/S M~3/S I...... I...... I...... I...... I...... I 5 R/FALL 10 EXCESS 15 MM 20 25 0 0. 0. 1 0. 0. * 2 0. 0. * 3 0. 0. * 4 0. 0. * 5 0. 0. * 6 7. 0. * 7 50. 0. *x 8 196. 25. *0 9 468 . 740. *-- 10 819. 850. 11 1147. 920. * 12 1348 . 980. * 13 1403. 1050. * 14 1374. 1070. * 15 1309. 1100. * 16 1224. 1110. * — 17 1126. 1140. * 18 1028 . 1180. * X O 9 961. 1220. * X O 20 960. 1250. * _ X O 21 1023. 1250. * - X 0 22 1115. 1240. * X O 23 1191. 1250. * X O ' 24 1226. 1240. * O 25 1207 . 1250. *— XO 26 1146. 1180. * — XO 27 1059. 1140. XO 28 967 . 1130. * X O 29 884. 1100. * X o 30 846 . 1090. * X o 31 910. 1160. * X o 32 1095. 1360. * X o 33 1392. 1640. * X O 34 1684 . 1920. * X 0 35 1847 . 2100. * X O 36 1910. 2220. * X 0 37 1942. 2290. * — X 0 ^8 1963. 2340. * - X O 39 1943. 2290. * X 0 40 1860. 2200. * _ X O 41 1730. 2080. * O 42 1578. 1960. * O 43 1423. 1820. * 0 44 1273. 1630. * O 45 1133. 1470. * 46 1008. 1300. * 47 901. 1150. * 48 812. 1020. * 49 739. 890. * 50 680. 750. * 51 632. 650. rt 52 592. 480. * 53 557. 370. rt 0 X 54 524. 265. * O X 55 493. 170. rt 0 X 56 462. 110. * o X 57 430. 60 . *0 X 58 399. 0. rt X 59 368 . 0. rt X 60 339. 0. * X I ..... I...... I...... I I...... I iVij JJ/ ii x 1/ J-vwvj it 11 uuui iniv jl

TIME PERIOD (HOURS) 3.00

DEPTH EXCESS RAIN (MM) 63.93

DEPTH CALC. HYDROGRAPH (MM) 63.82 CALC. PEAK DISCHARGE (M3/S) 2127.39 iCALC. TIME TO PEAK (HOURS) 108.00 CALC. HYDROGRAPH DELAYED (HOUR)= 0.00

RECD PEAK DISCHARGE (M3/S) = 2340.00 RECD TIME TO PEAK (HOURS) = 114.00

RAINFALL DEPTHS (MM): 61 103 90 269 351 511 195 TIME CALCULATED RECORDED RAINFALL HYETOGRAPH HOUR M3/S M3/S MM/PERIOD 0.00 0.00 0.00 * ** * * * 3.00 0.00 0.00 4 3 0 7 14 16 0 6.00 0.00 0.00 7 7 1 11 21 47 1 9.00 0.00 0.00 4 4 26 15 37 43 7 12.00 0.00 0.00 14 14 12 10 55 60 0 15.00 15.26 0.00 2 1 8 13 24 50 15 8.00 117.22 0.00 0 1 7 12 15 9 11 21.00 323.06 0.00 1 2 1 2 9 13 11 24.00 610.24 25.00 6 4 9 25 37 43 35 27.00 990.82 740.00 4 1 13 15 8 7 3 30.00 1310.02 850.00 1 0 3 4 2 0 1 33.00 1436.64 920.00 1 5 1 9 0 1 0 36.00 1423.57 980.00 0 4 0 9 2 1 2 39.00 1336.96 1050.00 1 3 1 9 2 2 2 42.00 1214.77 1070.00 0 3 0 8 2 2 2 45.00 1087.04 1100.00 1 3 0 8 1 2 2 48.00 965.56 1110.00 0 3 0 8 1 1 1 51.00 866.44 1140.00 1 4 2 9 3 5 9 54.00 866.27 1180.00 2 5 2 12 19 29 11 57.00 972.42 1220.00 0 0 0 1 13 8 1 60.00 1115.56 1250.00 1 2 1 4 1 13 4 63.00 1259.11 1250.00 1 2 1 4 2 7 4 66.00 1345.91 1240.00 0 1 1 3 2 3 3 69.00 1352.29 1250.00 0 1 0 3 2 2 3 ^2.00 1291.43 1240.00 0 1 0 3 3 2 2 ,5.00 1193.20 1250.00 0 2 0 3 3 2 1 78.00 1108.71 1180.00 0 0 0 4 4 5 9 81.00 1037.82 1140.00 0 0 0 1 0 2 3 84.00 962.74 1130.00 0 0 0 3 0 0 6 87.00 983.03 1100.00 1 2 1 4 0 32 5 90.00 1193.52 1090.00 3 3 0 3 20 29 4 93.00 1488.62 1160.00 1 3 0 2 2 10 3 96.00 1698.80 1360.00 0 1 0 3 2 5 6 99.00 1858.51 1640.00 1 3 0 6 16 12 17 102.00 2003.14 1920.00 2 6 1 0 4 20 8 105.00 2087.34 2100.00 1 1 0 5 10 11 0 108.00 2127.39 2220.00 1 3 1 12 5 12 1 111.00 2124.53 2290.00 0 0 0 6 3 4 2 114.00 2043.10 2340.00 0 1 0 1 3 0 0 117.00 1895.52 2290.00 0 2 0 5 2 1 0 120.00 1722.08 2200.00 0 2 0 5 2 4 0 123.00 1558.86 2080.00 0 0 0 0 0 0 0 126.00 1408.91 1960.00 0 0 0 0 0 0 0 129.00 1272.16 1820.00 0 0 0 0 0 0 0 132.00 1150.78 1630.00 0 0 0 0 0 0 0 135.00 1044.26 1470.00 0 0 0 0 0 0 0 138.00 950.51 1300.00 0 0 0 0 0 0 0 141.00 867.08 1150.00 0 0 0 0 0 0 0 144.00 791.81 1020.00 0 0 0 0 0 0 0 TO CL) > x: CD a) 7 CD in CO O JD 13 CD □ H ours)

S

(x

PERIODS

TIME APPENDIX D

SUMMARY

OF

RESULTS TABLE D.1 (contd) TWEED RIVER TO MURWILLUMBAH

(b) Initial and continuing losses as per Table 5.1(a)

Actual Unit RORB WBNM Event QP Time QP Time QP Time QP Time

1 1340 27 1410 30 1550 30 1360 27 la)105 b) +3 116 + 3 101 0

2 850 33 790 33 790 33 750 33 93 0 93 0 88 0

3 1000 48 1130 48 1090 48 880 48 113 0 109 0 88 -3

4 950 30 880 36 820 27 810 27 84 + 6 86 -3 85 -3

5* 1330 33 ------

6 * 1240 24 ------

7 1620 21 2180 24 2570 21 1810 24 135 + 3 159 0 112 + 3 1010 69 1010 69 770 69 620 69 100 0 76 0 61 0

8* 1410 60 ------

9 1100 18 1150 21 1100 18 1120 18 105 + 3 100 0 102 0

10 1030 27 950 24 1020 24 770 24 89 -3 99 -3 75 -3 880 45 1000 48 1220 45 1060 45 114 + 3 139 0 120 0

Average 104 + 1.7 109 -0.3 92 - -0.3 Standard Deviation 15 2.6 26 1.8 18 2.8 Correlation Coef f 0.96 0.92 0.89

* Test events not used in derivation of statistical parameters

(a) Qp(Model/Actual) (%) (b) Time Difference (Model - Actual) (hrs) TABLE D.2 WILSONS RIVER TO LISMORE

Unit hydrograph: Average of fit events(Refer to Table 5.3) RORB Parameters: KC = 94, m = 0.8

(a) Initial loss as per Table 5.1(b) Median continuing loss = 2.0 rnm/hr

Actual Unit RORB Event QP Time QP Time QP Time

1 1430 45 1280 45 1030 48 (a) 90 b) 0 72 + 3

2 1310 ' 45 1560 42 1120 48 119 -3 85 + 3

3 460 42 460 36 260 51 100 -6 57 + 9

4 * 340 60 610 60 470 63 179 0 138 + 3

5 1050 63 1070 57 690 63 102 -6 66 0

6 * 270 30 Ijosses t:oo highl 260 21 no rimof f 100 -9

7 1140 75 1340 69 1070 72 118 + 6 94 -3

8 * 1150 51 520 54 530 60 45 + 3 46 + 9

9 550 42 570 39 300 51 104 -3 55 + 9

10 1320 51 1660 48 1440 42 126 -3 109 -9

11 880 81 590 72 420 81 67 -9 48 0

Average 103 -3.0 73 + 1.5 Standard Deviation 19 4.5 21 6.0 Correlation Coef f 0.91 0.91 TABLE D.2 (contd) . WILSONS RIVER TO LISMORE

(b) Initial and continuing losses as per Table 5.1(b)

Actual Unit RORB Event QP Time QP Time QP Time

1 1430 45 1480 45 1230 48 la)103 lb) 0 86 + 3

2 1310 45 1460 42 1030 48 111 -3 79 + 3

3 460 42 340 36 210 51 . 74 -6 46 + 9

4 * 340 60 - - - -

5 1050 63 1330 57 940 63 127 -6 ' 90 0

6 * 270 30 - - - -

7 1140 75 1090 69 860 75 96 -t-6 75 0

8 * 1150 51 - - - -

9 550 42 720 39 400 51 131 -3 73 4-9

10 1320 51 1330 48 1120 42 101 -3 85 -9

11 880 81 980 72 790 78 111 -9 90 -3

Average 107 -3.0 78 + 1.5 Standard Deviation 18 4.5 14 6.0 Correlation Coef f 0.95 0.98

* Test events not used in derivation of statistical parameters

(a) Qp(Model/Actual) (%) (b) Time Difference (Model - Actual) (hrs) TABLE D.3 MACLEAY RIVER TO KEMPSEY

Unit hydrograph: Average of fit events(Refer to Table 5.3) RORB Parameters: KC = 210, m = 0.8 WBNM Parameters: C = 1.9, x = 0.32

(a) Initial loss as per Table 5.1(c) Median continuing loss = 1.5 mm/hr for U/H Median continuing loss = 1.9 mm/hr for RORB and WBNM

Actual Unit RORB WBNM Event QP Time QP Time QP Time QP Time

1 3670 66 4370 69 4400 66 4270 63 (a)119 (b) +3 120 0 116 -3

2 3130 51 4590 63 3440 ' 57 3540 51 147 + 12 110 + 6 113 0

3 * 1840 51 1640 45 1630 48 89 -6 89 -3

4 3100 51 1635 48 1650 51 1250 48 53 -3 53 0 40 -3 2470 93 Second £ueak not model] .ed 2400 120 620 129 2190 132 830 132 26 + 9 91 + 12 35 + 12

5 * 3260 54 3760 66 3310 51 115 + 12 102 -3 3170 99 2470 102 2720 78 78 + 3 86 -21

6 1250 60 1630 45 1100 39 870 66 130 -15 88 -21 70 + 6 2340 114 640 117 1220 114 1310 108 27 + 3 52 0 56 -6

7 * 2990 57 710 45 970 72 24 -12 32 + 15

8 ..2890 93 1560 96 3480 84 2740 84 54 + 3 120 -9 95 -9

9 2290 69 3280 66 2350 69 1940 66 143 -3 103 0 85 -3

10 3190 69 6120 78 4300 69 4100 66 192 + 9 135 0 129 -3

11 2920 63 2950 57 2300 51 2150 48 101 -6 79 -12 74 -15

Average 99 + 1.2 95 -2.4 81 -2.4 Standard Deviation 57 8.1 28 9.4 32 7.5 Correlation Coef f 0.55 0.76 0.75 TABLE D.3 (contd) MACLEAY RIVER TO KEMPSEY

(b) Initial and continuing losses as per Table 5.1(c)

Actual Unit RORB WBNM Event QP Time QP Time QP Time QP Time

1 3670 66 4370 69 3980 66 3890 60 (a)119 (b) +3 108 0 106 -6

2 3130 51 3410 63 2710 57 2790 51 109 4-12 87 + 6 89 0

3 * 1840 51 - - - -

4 3100 51 3290 51 2500 51 2170 48 106 0 81 0 70 -3 2470 93 Second peak not: model].ed 2400 120 2570 129 1900 135 2190 132 107 + 9 77 + 15 91 + 12

5 * 3260 54 - _ _ —

3170 99 - - - -

6 1250 60 1630 48 1400 39 1350 69 17 2 -12 112 -21 108 + 9 2340 114 1700 120 1940 114 2130 108 73 + 6 83 0 91 -6

7 * 2990 57 - - --

8 2890 93 3300 96 3790 84 3070 84 114 + 3 131 -9 106 -9

9 2290 69 2440 66 2140 69 1730 66 107 -3 93 0 76 -3

10 3190 69 2670 78 2860 72 2400 ' 69 84 + 9 90 + 3 75 0

11 2920 63 3080 57 2780 51 2630 48 105 -6 95 -12 90 -15

Average 110 + 2.1 94 -2.7 90 -2.1 Standard Deviation 26 7.5 17 10.0 14 8.0 Correlation Coef f 0.87 0.83 0.84

* Test events not used in derivation of statistical parameters

(a) Qp(Model/Actual) (%) (b) Time Difference (Model - Actual) (hrs)